1. Field of the Invention
The invention relates to a method for image processing, particularly to a method for tracking image.
2. Description of the Prior Art
In the conventional technological field of image tracking, such as shown in U.S. Pat. No. 5,402,118, “Method and apparatus for measuring traffic flow”, U.S. Pat. No. 7,200,266, “Method and apparatus for automated video activity analysis”, and U.S. Pat. No. 6,259,802, “Object tracking technique using polyline contours”, the above-mentioned patents provide the reference background image and the instant image to be normally employed to compare and calculate the difference, and then drawing the tracked object contour or using shading value for tracking and detecting. While adopting the above-mentioned calculation method, the camera will activate the automatic white balance function in order to carry on the work in the all-weather environment. As shown in U.S. Pat. No. 7,199,821, “Imaging apparatus and method for controlling white balance”, various parameters of white balance and shutter will be adjusted immediately according to the characteristics of the image at that time. When the luminance of picture is too bright, the parameters will be adjusted to reduce inlet light quantity. When the luminance of picture is too low, the inlet light quantity will be increased so that the color of whole picture can reach a steady state.
After the white balance function of camera is activated, the background and tone of detected object will be changed; also will influence the tracking accuracy of image. For example, when the large vehicles pass through the detected area of camera, the white balance function of camera will be activated soon. Due to the whole detected area of camera becoming totally color occupation by the large vehicles, therefore the image of camera would be whole changed, also the detected object is unable to be judged accurately. Furthermore, the large vehicles usually pass through the outer traffic lane, thus the effective detection for the image of roadside vehicle detector will also be influenced.
Besides using white balance function of the above-mentioned camera to process the image tracking, there are other processing ways for the change caused by the natural weather and light. That is, also in the conventional image treatment, the image is adjusted by using image background renewing method.
As shown in Taiwan Patent I220,969, the detected image and initial background image can be compared to obtain a difference value. When the difference value is higher than a threshold value, it will be necessary to be upgraded. However, the upgrade speed of the above-mentioned method is quite slow, which is unable to process the change of light properly and instantly.
In order to respond the requirement of image tracking, the invention develops the relevant technologies for tracking and calibration of image, to improve the tracking result, to save the cost of manpower and time, and to promote the development of relevant technologies.